Due to the prosperity of cloud computing, it is predicted that transition from possession of IT to use of IT will be progressed in companies. Under the circumstances, there are more vendors that provide storage services through the Internet. Representative examples of the online storage services include Amazon S3 and Windows (registered trademark) Azure Storage. In general, Web interfaces, such as REST and SOAP, are used to access the online storage services, and fees are charged according to the amount of use of resources. Although problems of security and compliance remain, there is a large advantage in terms of cost. Therefore, it is expected that the use will significantly expand.
In the use of such external online storage services, there is a problem that the amount of charge increases with an increase in the amount of saved data. Since the data is transferred through a WAN, the transfer efficiency is not excellent, and there is a problem that it takes time to save a large amount of data. Furthermore, the fees are charged not only for an amount of storage, but also for an amount of transfer. Therefore, compression of saved and transferred data is an important technique.
Algorithms, such as GZIP and LZH, are typical for systems of data compression in storage. However, in recent years, a system for integrating duplicated data to eliminate a degree of data duplication to realize compression is proposed. For example, an invention of Patent Literature 1 proposes a system in storing a plurality of OS images in a SAN storage, wherein duplication of a common section of the OS images is eliminated to realize a reduction in the storage capacity. In the patent, the storage is divided into a common LU and an individual LU. OS and AP data common to the hosts is stored in the common LU, and host individual data is stored in the individual LU. In this way, duplication is eliminated for the OS and AP data that would be duplicated in conventional techniques, and a reduction in the storage capacity is realized.